Griffith, Austin G., Ryan K. W. Lau, Jaime Cardenas, Yoshitomo Okawachi, Aseema Mohanty, Romy Fain, Yoon Ho Daniel Lee, et al.. “Silicon-chip mid-infrared frequency comb generation.” Nature Communications 6 (2015). Abstract
Optical frequency combs are a revolutionary light source for high-precision spectroscopy because of their narrow linewidths and precise frequency spacing. Generation of such combs in the mid-infrared spectral region (2-20 mm) is important for molecular gas detection owing to the presence of a large number of absorption lines in this wavelength regime. Microresonator-based frequency comb sources can provide a compact and robust platform for comb generation that can operate with relatively low optical powers. However, material and dispersion engineering limitations have prevented the realization of an on-chip integrated mid-infrared microresonator comb source. Here we demonstrate a complementary metal-oxide-semiconductor compatible platform for on-chip comb generation using silicon microresonators, and realize a broadband frequency comb spanning from 2.1 to 3.5 mm. This platform is compact and robust and offers the potential to be versatile for use outside the laboratory environment for applications such as real-time monitoring of atmospheric gas conditions.
Graphene electro-optic modulator with 30 GHz bandwidth
Phare, Christopher T., Yoon-Ho Daniel Lee, Jaime Cardenas, and Michal Lipson. “Graphene electro-optic modulator with 30 GHz bandwidth.” Nature Photonics 9 (2015): 511. Abstract
Graphene has generated exceptional interest as an optoelectronic material(1,2) because its high carrier mobility(3,4) and broadband absorption(5) promise to make extremely fast and broadband electro-optic devices possible(6-9). Electro-optic graphene modulators previously reported, however, have been limited in bandwidth to a few gigahertz(10-15) because of the large capacitance required to achieve reasonable voltage swings. Here, we demonstrate a graphene electro-optic modulator based on resonator loss modulation at critical coupling(16) that shows drastically increased speed and efficiency. Our device operates with a 30 GHz bandwidth and with a state-of-the-art modulation efficiency of 15 dB per 10 V. We also show the first high-speed large-signal operation in a graphene modulator, paving the way for fast digital communications using this platform. The modulator uniquely uses silicon nitride waveguides, an otherwise completely passive material platform, with promising applications for ultra-low-loss broadband structures and nonlinear optics.
Cardenas, Jaime, Mian Zhang, Christopher T. Phare, Shreyas Y. Shah, Carl B. Poitras, Biswajeet Guha, and Michal Lipson. “High Q SiC microresonators.” Optics Express 21 (2013): 16882-16887. Abstract
We demonstrate photonic devices based on standard 3C SiC epitaxially grown on silicon. We achieve high optical confinement by taking advantage of the high stiffness of SiC and undercutting the underlying silicon substrate. We demonstrate a 20 mu m radius suspended microring resonator with Q=14,100 fabricated on commercially available SiC-on-silicon substrates. (C) 2013 Optical Society of America